1. Requirements for monitoring the global tropopause Bill Randel Atmospheric Chemistry Division NCAR

2. Tropopause is most simply identified by a change in stability (lapse rate) midlatitude tropopause tropical tropopause

3. Latitudinal structure of the tropopause

4. Tropopause separates air masses with different dynamical and chemical characteristics Ozone

5. definitions of the tropopause Lapse rate tropopause (WMO definition) Cold point (most relevant in the tropics) Specific value of potential vorticity (PV=2) advantage: continuously valued, useful for dynamics/transport studies disadvantage: requires meteorological analysis; cannot calculate from temp profiles alone

6. What are the science issues re: tropopause and climate? Is the tropopause a sensitive indicator of climate change? (if so, what parameters?) How is the tropopause related to long-term ozone variability?

7. Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes Santer et al. Science, July 2003 increase in global tropopause height of ~0.2 km

8. observations (NCEP data) climate model with changing CO2, ozone, aerosols,... decrease in tropopause pressure (increase in altitude) Spatial ‘fingerprint’ of tropopause changes

9. caveat: vertical resolution of models and (some) observations can be ~2 km ~ 2 km

10. Correlation of ozone and tropopause height on short and long time scales WMO, 2002 updated from Steinbrect et al 2001 column ozone and tropopause height at Hohenpeissenberg

11. What are the requirements to monitor the tropopause? Key point is vertical resolution (plus spatial sampling) compare statistics for different measurements: * radiosondes * GPS radio occultation (GPS/MET, CHAMP, SAC-C) * operational analyses / reanalyses (ERA40, NCEP)

12. High resolution radiosonde profile

13. statistical distribution of tropopause heights from radiosondes at Pittsburgh 1994-2003 note two maxima January

14. seasonal variation at Pittsburgh 1994-2003 JanuaryJuly

15. lowest tropopause at Pittsburgh 1994-2003 JanuaryJuly

16. seasonal cycle in tropopause height

17. How do tropopause statistics depend on vertical resolution? radiosondes GPS

18. Sondes vs. ERA40 and NCEP radiosonde ERA40 (60-level) NCEP (17-level)

19. Tropopause statistics from reanalyses radiosondes ERA40 (60-level) NCEP (17-level) note lower resolution

20. seasonal variation from different data sources

21. Other statistics: occurrence of multiple tropopauses example from GPS data

22. from Pan et al., JGR, 2004 zonal wind (from analysis) tropopause from aircraft profiler measurements potential vorticity (from analysis) double tropopause associated with break near subtropical jet

23. aircraft ozone measurements tropopause break associated with stratospheric intrusion

24. seasonal variation of profiles with multiple tropopauses radiosondesGPS

25. Spatial pattern of multiple tropopauses from GPS data January

26. occurence of multiple tropopauses in January GPS NCEP ERA40 undersampled by lower resolution

27. long-term variability in occurrence of multiple tropopauses fraction of soundings with multiple tropopause

28. long-term variability in occurrence of multiple tropopauses number of levels in sounding fraction of soundings with multiple tropopause

29. Key points: Vertical resolution important for tropopause statistics (anticipated changes are small...0.1 km/decade) Similar statistics derived from radiosondes, GPS and 60-level ERA40 data (resolution ~0.5 – 1.0 km) Lower resolution analyses (~ 2 km) undersample variability Tropopause closely linked to ozone variability Homogenity of data records will likely influence statistics

30. Increased vertical resolution after ~1995 lower resolutionhigh resolution

31. 12 km ‘snapshot’ of ozone from MOZART3 Courtesy Doug Kinnison